Flat panel display device with first electrode having concentration gradient and fabrication method thereof

ABSTRACT

A method of fabricating a flat panel display comprises forming a first electrode, forming at least one organic electroluminescent layer on the first electrode, forming an second electrode, wherein the first electrode comprises a first component of a transparent material and a second component of a metallic material, and the forming of the first electrode comprises depositing the first and second components so as to have a gradual concentration gradient in which the first component is decreased while the second component is increased at a part in contact with the exposed electrode, according to a thickness of the first electrode. The first electrode functions as a pixel electrode and a black matrix of the flat panel display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/895,925,filed Jun. 22, 2004, now U.S. Pat. No. 6,902,943. This applicationclaims the benefit of Korean Patent Application No. 2001-85210 filed onDec. 26, 2001, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flat panel display device, and moreparticularly, to a front light emitting type organic electroluminescentdisplay device with a first electrode having a concentration gradientwhich functions as a pixel electrode and a black matrix at the sametime, and a method of fabricating the front light emitting type organicelectroluminescent display device.

2. Description of the Related Art

FIG. 1A illustrates the cross-sectional structure of a conventionalfront light emitting type organic electroluminescent (EL) displaydevice. FIG. 1B illustrates the plan structure of a conventional organicelectroluminescent display device. FIG. 1A illustrates thecross-sectional structure taken along the line I—I of FIG. 1B.

Referring to FIG. 1A and FIG. 1B, a transparent insulation substrate 10is divided into a first region 11 in which a pixel electrode is formed,and a second region 12 in which a thin film transistor (TFT) and acapacitor are formed. The second region 12 includes a semiconductorlayer 20 in which source/drain regions 21 and 22 are formed, a thin filmtransistor equipped with a gate electrode 31 and source/drain electrodes51 and 52, and a capacitor equipped with a first electrode 32, and asecond electrode 53 connected to the source electrode 51 of the thinfilm transistor.

A gate insulating layer 30 is formed in a space between thesemiconductor layer 20 and the gate electrode 31.

An interlayer insulating layer 40 is formed in a space between the gateelectrode 31 and the source/drain electrodes 51 and 52.

A pixel electrode 70 connected to one of the source/drain electrodes 51and 52, e.g., the drain electrode 52 through a via hole 61, is formed ona passivation layer 60 of the first region 11 as an anode electrode. Aplanarization layer 80 equipped with an opening part 81 which exposes aportion of the pixel electrode 70 is formed on the pixel electrode 70.An organic EL layer 90 is formed in the opening part 81, and atransparent electrode 95 is formed on the organic EL layer 90 as acathode electrode.

References 35, 55 and 56 of FIG. 1B represent gate lines, data lines andpower supply lines, respectively.

In the above described conventional front light emitting type organicelectroluminescent display device, contrast deteriorates because amaterial having a high reflection ratio is used, thereby reflecting anexternal light through a metal wiring material, particularly a metallicmaterial for source/drain electrodes.

Although the external light can be prevented from being reflected byadhering a polarizer onto a front of the conventional organicelectroluminescent display device, using the polarizer is expensive, anda luminance of the organic electroluminescent display device is loweredbecause a transmittancy of light emitted from an organicelectroluminescent (EL) layer of the organic electroluminescent displaydevice is lowered by the polarizer. Furthermore, a life cycle of theorganic EL layer is shortened where a current flowing through theconventional organic electroluminescent display device is increased toimprove the luminance of the organic electroluminescent display device.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a flatpanel display device having a black matrix which prevents reflection ofan external light.

Another object of the present invention is to provide a simplifiedmethod of fabricating a flat panel display device where a black matrixand a pixel electrode of the flat panel display device aresimultaneously formed by using a conductive layer having a predeterminedconcentration gradient of a transparent conductive material and ametallic material.

Yet another object of the present invention is to provide a flat paneldisplay device which prevents formation of a surface profile due to ause of a black matrix, and a method of fabricating the flat paneldisplay device thereof.

Still another object of the present invention is to provide a flat paneldisplay device which reduces a surface resistance and a contactresistance of source/drain electrodes by using an Al series material asthe source/drain electrodes, and a method of fabricating the flat paneldisplay device thereof.

Additional objects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

To achieve the above and other objects of the present invention, thereis provided a method of fabricating a flat panel display, the methodcomprising forming a first electrode; forming at least one organicelectroluminescent layer on the first electrode; forming a secondelectrode; wherein the first electrode comprises a first component of atransparent material and a second component of a metallic material, andthe forming of the first electrode comprises depositing the first andsecond components so as to have a gradual concentration gradient inwhich the first component is decreased while the second component isincreased at a part in contact with the exposed electrode, according toa thickness of the first electrode.

According to an aspect of the present invention, the first electrodefunctions as a black matrix as well as a pixel electrode of the displaydevice.

The first component of the first electrode may be one of ITO, IZO andZnO, and the second component thereof may be one of Al, Cr, Mo, Ti, Ag,Au and W. The first electrode may be deposited by one of co-sputteringand co-evaporating the transparent first material and the metallicsecond material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1A is a cross-sectional view of a conventional organicelectroluminescent display device;

FIG. 1B is a plan view of the conventional organic electroluminescentdisplay device shown in FIG. 1A;

FIG. 2A is a cross-sectional view of an organic electroluminescentdisplay device according to an embodiment of the present invention;

FIG. 2B is a plan view of the organic electroluminescent display deviceshown in FIG. 2A; and

FIG. 3 is a drawing illustrating concentration gradients of atransparent conductive material and a metallic material of a firstelectrode that is used as a pixel electrode and a black matrix in anorganic electroluminescent display device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIG. 2A shows a cross-sectional view of an organic electroluminescentdisplay device according to an embodiment of the present invention, andFIG. 2B shows a plan view of the organic electroluminescent displaydevice, wherein the FIG. 2A illustrates a cross-sectional structuretaken along the line II—II of FIG. 2B.

Referring to FIG. 2A and FIG. 2B, the display device includes aninsulation substrate 100 having a first region 101 to form a pixelelectrode, and a second region 102 to form a thin film transistor (TFT)and a capacitor. A buffer layer 115 is formed on the insulationsubstrate 100. The thin film transistor (TFT) is formed in a secondregion 102 of the insulation substrate 100. The TFT comprises asemiconductor layer 120 equipped with n or p type source/drain regions121 and 122, a gate electrode 131, and source/drain electrodes 141 and142, each of which is connected to the source/drain regions 121 and 122through contact holes 136 and 137, respectively.

A capacitor having a first electrode 132 and a second electrode 143connected to the source electrode 141 are formed in the second region102. Each of insulation layers, e.g., a gate insulation layer 135 and aninterlayer insulation layer 145, are formed in a space surrounded by thesemiconductor layer 120, gate electrode 131 and first electrode 132, anda space surrounded by the gate electrode 131, first electrode 132 andsource/drain electrodes 141 and 142, respectively. A part between thefirst electrode 132 and the second electrode 143 in the interlayerinsulation layer 145 functions as a capacitor dielectric layer.

A passivation layer 150 is formed on the interlayer insulation layer 145equipped with the TFT and the capacitor. A via hole 155, which exposes apart of one electrode out of the source/drain electrodes 141 and 142,e.g., the drain electrode 142, is formed by etching the passivationlayer 150.

A first electrode 160 connected to the drain electrode 142 through thevia hole 155 is formed on the passivation layer 150. An opening part 175which exposes a part corresponding to a first region in the firstelectrode 160 is formed after forming an insulation layer 170 on a frontface of the insulation substrate 100. An organic EL layer 180 is formedon the first electrode 160 exposed by the opening part 175, and acathode electrode is formed on the organic EL layer 180 as a transparentelectrode 190.

The insulation layer 170 formed on the passivation layer separation wallwhich prevents a short, and separates each of pixels of a pixelelectrode (described herein below) under the insulation layer 170.

The first electrode 160 functions as an anode electrode which is a pixelelectrode of the organic electroluminescent display device, as well as ablack matrix which prevents reflection of an external incident light.Since the transparent electrode 190 is used as a cathode electrode, amaterial having a smaller work function from that of the first electrode160, which functions as a pixel electrode, is used as a material for thetransparent electrode 190.

FIG. 3 shows concentration gradients of a transparent conductivematerial and a metallic material of the first electrode 160. The firstelectrode 160 includes a first component of a transparent conductivematerial and a second component of a metallic material, and has agradual concentration gradient corresponding to a deposition thicknessof the first electrode 160.

That is, as illustrated in FIG. 3, the first electrode 160 is depositedin such a manner that the deeper an incidence depth “r” of externallight is in an incidence direction, a concentration gradient of thefirst component of the transparent conductive material is graduallydecreased while a concentration gradient of the second component of themetallic material is gradually increased. The rate of decrease/increaseand the arrangement of the concentration gradients depend on adeposition thickness “d” of the first electrode 160, wherein thetransparent conductive material and the metallic material exist in analmost equal ratio at about a half deposition thickness of the firstelectrode 160.

As described in the above, absorption rather than reflection of theexternal incident light occurs in the first electrode 160 since acomposition ratio of the transparent conductive material and themetallic material is gradually and slowly changed by the gradualconcentration gradients of the transparent conductive material and themetallic material. Therefore, the first electrode 160 functions as ablack matrix which prevents reflection of the external light asreflection of the external light is inhibited by the first electrode160.

Indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), etc.,can used as a first component of a transparent conductive material ofthe first electrode 160, while Al, Cr, Mo, Ti, Ag, Au, W, etc., can usedas a second component of a metallic material of the first electrode 160.The first electrode 160 is deposited by, for example, simultaneouslycosputtering or coevaporating the metallic material and the transparentconductive material.

The first electrode 160 is deposited in such a manner that the deeper anincidence depth “e” of external light is, a transparent conductivematerial is gradually decreased while a metallic material is graduallyincreased, depending on a deposition thickness “d” of the firstelectrode 160. Accordingly, a part which contacts the drain electrode142 through the via hole 155, that is, a bottom of the first electrode160, is formed with a relatively high composition of the metallicmaterial while a part which contacts the organic EL layer 180, that is,an upper surface of the first electrode 160, is formed with a relativelyhigh composition of the transparent conductive material.

Therefore, although it has conventionally been difficult to use Alhaving a low resistivity as source/drain electrodes, due to diffusionproblems between Al and ITO (which is used as a transparent conductivelayer or a pixel electrode), an organic electroluminescent displaydevice of the present invention is capable of using Al as thesource/drain electrode material by using the first electrode 160, whichhas gradual concentration gradients of the transparent conductivematerial and the metallic material, as a pixel electrode.

That is, diffusion problems between Al and the pixel electrode do notoccur, although Al is used as the source/drain electrodes, since acomposition of the transparent conductive material is relatively low,and a composition of the metallic material is relatively high at a partwhere the first electrode 160 is in contact with the drain electrode142. Therefore, since Al can be used as the source/drain electrodes inan organic electroluminescent display device of the present invention, asurface resistance of the source/drain electrodes as well as a contactresistance between the pixel electrode and the source/drain electrodescan be reduced.

The first electrode 160 is conductive since it functions as the pixelelectrode and the black matrix at the same time. Therefore, the firstelectrode 160 should be separately formed per each pixel electrode of anorganic electroluminescent display device. An organic electroluminescentdisplay device according to the present invention has a structure inwhich a first electrode 160 is formed on a front surface of a pixelregion defined by gate lines 130, data lines 140 and power supply lines147, as illustrated in the planar structure of FIG. 2B. However, thestructure is not limited thereto, and it is understood that otherarrangements can be made so as to have the first electrode beelectrically separated between each of the pixels.

Although a first electrode 160 having gradual concentration gradients offirst and second materials is illustrated as both a pixel electrode anda black matrix with respect to a front light emitting type organicelectroluminescent display device, it is understood that the presentinvention can be applied to other display devices including a reflectiontype liquid crystal display device.

Additionally, a display device of the present invention can be an allorganic electroluminescent display device having an electrode layer,which does not transmit light from an organic thin layer formed betweentwo electrodes, that functions as a first electrode.

A formation of an organic electroluminescent (EL) display device of thepresent invention is simple because a pixel electrode and a black matrixof the organic EL display device are formed at the same time using aconductive layer having gradual concentration gradients of a transparentconductive material and a metallic material.

In an organic EL display device of the present invention, a luminance isimproved by preventing reflection of external light without the use ofan expensive polarizer. Additionally shorts between wirings areprevented by preventing the formation of a surface profile due to theformation of a black matrix.

Furthermore, an organic EL display device of the present invention iscapable of using Al having a low resistance as source/drain electrodes.A conductive layer, in which a part which contacts the source/drainelectrodes has a low composition of an ITO and a high composition of ametallic material, is used as a pixel electrode. Accordingly, anAl-series material can be used as the source/drain electrodes, and acontact resistance between the source/drain electrodes and the pixelelectrode is reduced.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A method of fabricating a flat panel display, the method comprising:forming a first electrode; forming at least one organicelectroluminescent layer on the first electrode; forming a secondelectrode; wherein the first electrode comprises a first component of atransparent material and a second component of a metallic material, andthe forming of the first electrode comprises depositing the first andsecond components so as to have a gradual concentration gradient inwhich the first component is decreased while the second component isincreased at a part in contact with the exposed electrode, according toa thickness of the first electrode.
 2. The method according to claim 1,wherein the first component of the first electrode is one of ITO, IZOand ZnO, and the second component is one of Al, Cr, Mo, Ti, Ag, Au andW.
 3. The method according to claim 2, wherein the depositing of thefirst electrode comprises one of cosputtering and coevaporating thefirst component and the second component.
 4. The method according toclaim 2, wherein the first electrode functions as a black matrix as wellas a pixel electrode of the display.
 5. The method according to claim 1,wherein the second electrode is transparent.
 6. The method according toclaim 5, wherein the second electrode comprises one of ITO, IZO and ZnO.